Jigsaw puzzles are formed by dividing a flat plate such as a flat paper sheet into multiple pieces onto which patterns of paintings, photographs, graphics, symbols, letters, characters and the like are drawn. Jigsaw puzzles are a toy which is enjoyed by assembling discrete pieces together to restore the pattern. Each piece is a flat plate having a polygonal shape such as a quadrangular shape and having, on the side face thereof, a male or female engaging member with an approximately round shape. A male engaging member of a piece can be interlocked with a female engaging member of another neighbouring piece. A female engaging member of a piece is interlocked with a male engaging member of another neighbouring piece.
The neighbouring pieces are formed so that the male engaging member fits the female engaging member. All pieces are formed so as to respectively have slightly different shapes and so that there are no two pieces having completely the same shape. According to this, a piece can be interlocked with only neighbouring pieces. Jigsaw puzzles are formed by drawing patterns on relatively thick flat materials mainly including paper, cork, wood and the like. Recently, jigsaw puzzles made of synthetic resins have been manufactured which have sharper patterns that are reminiscent of stained glass and the like.
Jigsaw puzzles are required to have a certain thickness in order to maintain the assembled state. Base sheets made of synthetic resins which form jigsaw puzzles need to have a thickness of 1.0 to 2.0 mm or more. However, it is difficult to continuously print patterns by currently available printing machines on base sheets that are 1.0 to 2.0 mm or more in thickness. Base sheets having a thickness of 1.0 to 2.0 mm or more are also difficult to be taken up onto rolls by winding devices. Accordingly it is also difficult to continuously print by web-fed printing machines. Conventional base sheets are laminates containing a flat sheet having the dimensions of the completed jigsaw puzzle as well as a certain thickness and a thin film on which a pattern is printed, which are bonded together by means of an adhesive and the like.
The present applicant has proposed a jigsaw puzzle made of a synthetic resin which is manufactured by printing on a hard sheet having a predetermined size on a sheet-fed offset printing machine, laminating the sheet with a soft flat sheet using an adhesive to obtain a puzzle substrate made of the synthetic resin having a thickness and stamping out the puzzle substrate into pieces on a stamping machine (see Patent Document 1). The puzzle substrate disclosed in Patent Document 1 is formed by bonding outer printed hard films on both sides of an inner soft sheet using an adhesive. The puzzle substrate is formed so that the inner soft sheet and outer hard films on both sides thereof are integrated and become a relatively thick single plate.
Pieces made of the synthetic resin disclosed in Patent Document 1 are not easily detached from one another when they are correctly assembled. Users can get, when they correctly interlock the pieces made of synthetic resins, a feeling that the pieces are a sure fit. In addition, the pieces made of synthetic resins which are correctly interlocked make a sound as if they are a sure fit, providing users with a sense of accomplishment as well as pleasurable sensation.
Patent Document 1: Japanese Patent Application Laid-open No. 2006-55290
However, the jigsaw puzzle disclosed in Patent Document 1 requires multiple steps for manufacturing, resulting in low workability and productivity. Specifically, multiple steps for manufacturing are required including the step of forming a puzzle substrate by uniformly applying an adhesive on an inner soft sheet formed to have a predetermined size depending on the size of a complete jigsaw puzzle; the step of forming a laminate by bonding, one by one, outer hard films having the size matching to the inner soft sheet before heating and pressing; and the step of pressing the formed laminate to form the puzzle substrate which is then stamped out on a stamping machine.
The jigsaw puzzle disclosed in Patent Document 1 requires separate bonding, one by one, of outer hard sheets having a matching size to the inner soft sheet having a certain size. The manufacturing method of the jigsaw puzzle disclosed in Patent Document 1 also requires uniform and even application of an adhesive, which is troublesome. The jigsaw puzzle disclosed in Patent Document 1 also requires uniform temperature of the plate and uniform application of pressure in order to uniformly set the adhesive, which are also troublesome. Thus the jigsaw puzzle disclosed in Patent Document 1 requires many troublesome working steps, resulting in high production costs. Namely, the jigsaw puzzle has such disadvantages that it has low workability and productivity, is not suitable for mass production and requires increased costs for production and manpower.